Changes of Food in the Tissues 147 



THE USE OF FOOD 



The revivified blood now passes to all parts of the 

 body and is brought into the most intimate relation with 

 the minutest portion of every tissue. Several things 

 happen in the course of time. 



In the first place, the new supply of nutritive sub- 

 stances is used by the living cells in a way we do not 

 wholly understand to rebuild worn-out tissue and to 

 form new growth. With the young animal, much 

 material is appropriated in the latter way. In the case 

 of the milch cow, there is furnished to the udder the 

 nutrients out of which the milk is formed through 

 the special activities of that gland. 



Moreover, it is in the tissues that the oxygen which 

 was taken up in the lungs is used to slowly burn a por- 

 tion of the food. This combustion is believed not to 

 take place by contact of the oxygen and food in the 

 large blood-vessels, but it occurs by progressive steps 

 throughout the minute divisions of the muscles and 

 other parts of the whole body. Notwithstanding this 

 oxidation may be very gradual and occupy much time, 

 its ultimate products are, for the most part, similar to 

 those which result from the rapid combustion of fuel. 

 In the fireplace, starch, sugar, cellulose, fats and similar 

 bodies would be burned to carbonic acid and water, and 

 this is what takes place in the animal to the extent 

 these nutrients are not used for growth. 



When the protein is not stored as such but is broken 

 up, the result differs somewhat in the furnace and in 

 the animal because in the latter the oxidation is not 



